Article having coating including compound of aluminum, boron and nitrogen

ABSTRACT

An article includes a monolithic substrate and a coating on the monolithic substrate. The monolithic substrate is selected from graphite, silicon carbide, silicon carbide nitride, silicon nitride carbide, and silicon nitride. The coating has a free, exposed surface and includes a compound of aluminum (Al), boron (B) and nitrogen (N) in a continuous chemically bonded network having Al—N bonds and B—N bonds. The compound includes an atom of nitrogen covalently bonded to an atom of boron and an atom of aluminum, and the compound has a composition B x Al (1-x) N, where x is 0.001 to 0.999.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/022,572, filed Mar. 17, 2016, which is a national phase ofInternational Application No. PCT/US2014/052450 filed Aug. 25, 2014,which claimed the benefit of U.S. Provisional Application No. 61/879,313filed Sep. 18, 2013.

BACKGROUND

Gas turbine engine components and other types of structures can befabricated from ceramic matrix composites. One type of ceramic matrixcomposite includes ceramic or carbon fibers distributed in a ceramicmatrix. The fibers can be coated with a relatively thin layer of boronnitride to protect the underlying fibers from environmental conditionsthat can cause chemical degradation.

SUMMARY

An article according to an example of the present disclosure includes asubstrate and a coating on the substrate. The coating includes acompound of aluminum (Al), boron (B) and nitrogen (N) in a continuouschemically bonded network having Al—N bonds and B—N bonds.

In a further embodiment of any of the foregoing embodiments, thecompound has a composition B_(x)Al_((1-x))N, where x is 0.001 to 0.999.

In a further embodiment of any of the foregoing embodiments, the coatingincludes an amount of B—N, by weight, of no greater than 50%.

In a further embodiment of any of the foregoing embodiments, thecontinuous chemically bonded network has a homogenous distribution ofthe Al—N bonds and the B—N bonds.

In a further embodiment of any of the foregoing embodiments, the Al—Nbonds and the B—N bonds are molecularly distributed such that thecontinuous chemically bonded network has a nanodispersion of domains ofthe Al—N bonds and the B—N bonds.

In a further embodiment of any of the foregoing embodiments, thesubstrate is a plurality of fibers.

In a further embodiment of any of the foregoing embodiments, the coatinghas a uniform thickness and consists of the compound of aluminum (Al),boron (B) and nitrogen (N).

In a further embodiment of any of the foregoing embodiments, the coatingincludes, by weight percent, a greater amount of aluminum (Al) thanboron (B).

In a further embodiment of any of the foregoing embodiments, thecompound includes an atom of nitrogen covalently bonded to atoms ofboron and aluminum.

An article according to an example of the present disclosure includes aplurality of fibers having a conformed coating thereon. The conformedcoating includes a compound of aluminum (Al), boron (B) and nitrogen (N)including Al—N bonds and B—N bonds, and a matrix in which the pluralityof fibers is disposed.

In a further embodiment of any of the foregoing embodiments, thecompound has a composition B_(x)Al_((1-x))N, where x is 0.001 to 0.999.

In a further embodiment of any of the foregoing embodiments, theconfirmed coating includes an amount of B—N, by weight, of no greaterthan 50%.

In a further embodiment of any of the foregoing embodiments, thecompound is a continuous chemically bonded network including the Al—Nbonds and the B—N bonds.

In a further embodiment of any of the foregoing embodiments, theplurality of fibers is selected from the group consisting ofsilicon-containing fibers, carbon fibers and combinations thereof.

In a further embodiment of any of the foregoing embodiments, theplurality of fibers is silicon carbide fibers.

In a further embodiment of any of the foregoing embodiments, theconformed coating contacts peripheral surfaces of central cores of thefibers.

In a further embodiment of any of the foregoing embodiments, the matrixis a silicon-containing material.

A method of protecting an article from environmental conditionsaccording to an example of the present disclosure includes protecting asubstrate that is susceptible to environmental chemical degradationusing a coating on the substrate. The coating includes a compound ofaluminum (Al), boron (B) and nitrogen (N) having Al—N bonds and B—Nbonds.

In a further embodiment of any of the foregoing embodiments, thecompound has a composition B_(x)Al_((1-x))N, where x is 0.001 to 0.999.

In a further embodiment of any of the foregoing embodiments, the coatingincludes an amount of B—N, by weight, of no greater than 50%.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of the present disclosure willbecome apparent to those skilled in the art from the following detaileddescription. The drawings that accompany the detailed description can bebriefly described as follows.

FIG. 1 illustrates an example article that includes a coating having acompound of aluminum, boron and nitrogen in a continuous chemicallybonded network having Al—N bonds and B—N bonds.

FIG. 2 schematically illustrates an example continuous chemically bondednetwork.

FIG. 3 illustrates another example article that includes fibers having aconformed coating thereon that has a compound of aluminum, boron andnitrogen with Al—N bonds and B—N bonds in a matrix.

FIG. 4 illustrates a representative one of the fibers of the article ofFIG. 3.

FIGS. 5A, 5B and 5C illustrate molecular level views of additionalexample compounds of aluminum, boron and nitrogen in a continuouschemically bonded network having Al—N bonds and B—N bonds.

FIGS. 6A and 6B illustrate molecular level views of additional examplecompounds of aluminum, boron and nitrogen in a continuous chemicallybonded network having Al—N bonds and B—N bonds.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a representative portion of an article20. It is to be understood that the article 20 is shown with a genericshape. However, the article 20 can be formed with a shape that isdesirable for the end-use application. For example, the article 20 canbe a gas turbine engine component, or portion thereof. Other types ofstructures that are exposed to relatively severe environmentalconditions can also benefit from this disclosure. As will be describedin more detail, the article 20 includes a specialized coating forprotecting an underlying substrate from environmental conditions thatcan otherwise cause accelerated chemical degradation.

In the illustrated example, the article 20 includes a substrate 22 and acoating 24 on the substrate 22. The coating 24 in this example iscontinuous, conforms to the shape of the substrate 22 and is of uniformthickness. The coating 24, also shown in schematic microscopic view inFIG. 2, includes a compound of aluminum, boron and nitrogen in acontinuous chemically bonded network 26 that has Al—N bonds 28 and B—Nbonds 30. As can be appreciated, the view shown in FIG. 2 is a highlyschematic representation of the chemical structure. The coating 24 canbe formed essentially of the compound of aluminum, boron and nitrogen,although in some examples, the coating 24 could include additionalphases or the coating 24 could include the compound of aluminum, boronand nitrogen in distinct, discrete regions that are dispersed though acontinuous phase of another material. However, it is expected that thecoating 24 formed only of, essentially of, or at least primarily of, thecompound of aluminum, boron and nitrogen will provide the most enhancedenvironmental protection to the substrate 22.

The composition of the compound of aluminum, boron and nitrogen can bevaried to alter thermal conductivity, oxidation resistance and possiblyother properties of the coating 24. In one example, the compound ofaluminum, boron and nitrogen has a composition B_(x)Al_((1-x))N, where xis 0.001 to 0.999. The prescribed composition yields, at least initiallyupon deposition, a single phase. The single phase is, however,inherently metastable and can phase separate under prolonged use of thearticle 20 at elevated temperatures into aluminum nitride and boronnitride phases. The composition B_(x)Al_((1-x))N and an amount of B—N,by weight, of no greater than 10% contribute to the thermal stability ofthe compound and ensures that, at least initially upon deposition, thecompound is a single phase. In this regard, the network 26, and thus thecoating 24, has a homogenous distribution of the Al—N bonds and the B—Nbonds. In other words, the Al—N and B—N are molecularly distributed suchthat the network 26 has a nanodispersion of domains of Al—N and B—N. Thecomposition B_(x)Al_((1-x))N and an amount of B—N, by weight, of nogreater than 50% are also preferred compositions for certain desirableproperties. In FIG. 2, these domains are represented at 32, and thenanodispersion of the domains 32 is represented by an average domainspacing 34 of one-hundred nanometers or less. Alternatively, thenanodispersion can be represented by an average maximum domain size ofone-hundred nanometers or less. The nanodispersion provides enhancedthermal conductivity and oxidation resistance, among other possiblebenefits.

In further examples of the composition B_(x)Al_((1-x))N, the Al—N andB—N are provided in a ratio, by weight. In some examples, the ratio canbe between 90:10 and 50:50, such as 75:25 or 50:50. Within the givenratio range, boron is always the least abundant. Aluminum is mostabundant at ratios of 90:10 and 75:25, and nitrogen is more abundantthan aluminum at the 50:50 ratio (43% N, 40% Al).

The enhanced thermal conductivity and oxidation resistance contribute toprotecting the underlying substrate 22 from environmental conditionsthat can otherwise cause chemical degradation of the material of thesubstrate 22, such as but not limited to oxidation. In some examples,the coating 24 is thus particularly useful for protecting substratesthat include materials that are susceptible to chemical degradationunder the expected environmental conditions in which the article 20 willbe used. For example, gas turbine engine components can be subjected toextreme elevated temperatures (e.g., above 750° C.) in the presence ofmoisture. In such conditions, the coating 24 protects the underlyingsubstrate 22 from chemical degradation. In one example, the substrate 22is a silicon-containing material or a carbon (e.g., graphite) material.In further examples, the substrate 22 is or includes silicon carbide. Infurther examples, the substrate 22 is or includes silicon carbidenitride, silicon nitride carbide or silicon nitride. The substrate 22can be a monolithic structure of these phases or a composite structurecontaining these phases.

FIG. 3 illustrates another example article 120. In this disclosure, likereference numerals designate like elements where appropriate andreference numerals with the addition of one-hundred designate modifiedelements that incorporate the same features and benefits of thecorresponding elements. In this example, the article 120 includes aplurality of fibers 122, a representative one of which is shown in FIG.4, and a matrix 136 in which the plurality of fibers 122 are disposed.As can be appreciated, the fibers 122 can be provided in any desirablefiber structure within the article 120, such as, but not limited tounidirectional arrangements, woven arrangements or other arrangements.

As shown in FIG. 4, the fibers 122 serve as the substrate and have aconformed coating 124 thereon. The conformed coating 124 continuouslysurrounds the fiber 122, conforms to the shape of the fiber 122 and isof uniform thickness. In this example, the coating 124 contactsperipheral surfaces 122 a of central cores of the fibers 122. That is,there are no intervening coatings between the fibers 122 and the coating124, although an intervening layer(s) is not precluded. Similar to thecoating 124 of FIG. 1, the conformed coating 124 includes a compound ofaluminum, boron and nitrogen that has Al—N bonds and B—N bonds. In onefurther example, the compound of the aluminum, boron and nitrogen is acontinuous chemically bonded network having the Al—N bonds and the B—Nbonds, as described above and shown in FIG. 2.

In a further example, the fibers 122 are selected fromsilicon-containing fibers, carbon fibers or combinations thereof. Inparticular, silicon-containing fibers, such as silicon carbide fibers,silicon nitride carbide fibers, silicon carbide nitride fibers andsilicon nitride fibers, and carbon (e.g., graphite) fibers can besusceptible to environmental conditions that chemically degrade thesilicon-containing material or carbon. In this regard, the conformedcoating 124 protects the underlying fiber 122 from chemical degradation.

The matrix 136 of the article 120 can also include the same or differentsilicon-containing material. For example, the silicon-containingmaterial of the matrix 136 is a continuous or discontinuous phase ofsilicon carbide, silicon carbide nitride, silicon nitride carbide orsilicon nitride. Alternatively, the matrix 136 is or includes othercontinuous or discontinuous phases, such as but not limited to carbides,nitrides, oxides, oxycarbides, oxynitrides, phosphides, sulfides orcombinations thereof. Additionally, the matrix 136 can be monolithic orcan be a composite of several phases of different compositions.

The coating 24/124 can be deposited onto the substrate 22/122 using anyor all of a variety of different deposition techniques. In one example,the coating 24/124 is deposited using a vapor deposition techniqueinvolving organometallic and metal organic precursors. For instance, theprecursors are Me₃NAlH₃ and NH₃BH₃. In another example, the coating24/124 can be deposited using a polymer deposition technique. Forinstance, the polymer deposition technique involves the deposition of apolymer from a reaction of tris-ethylaminoborane with diethyl aluminumamide, followed by pyrolysis or co-deposition in ammonia. Otherdeposition methods such as those based on deposition followed byreaction are also contemplated (e.g. deposition from analuminum-containing salt solution followed by nitridation with ammonia).

The above techniques can be used to deposit the compositions asdisclosed above, including the composition B_(x)Al_((1-x))N, where x is0.001 to 0.999. The deposition parameters can be controlled to controlthe value of x in the given composition. Depending upon the value of x,a single phase of the compound of aluminum, boron and nitride can bedeposited. Thus, by controlling the deposition parameters and value of xin the composition, a single phase of the coating 24/124 can bedeposited, as well as compounds of aluminum, boron and nitrogen that aredual phase of boron nitride and aluminum nitride. The depositionparameters and value of x can also be controlled to modify the extentand type of crystallinity of the compound in the coating 24/124. Inaddition to the deposition process and materials used, parameters suchas deposition time, temperature and atmosphere are the primaryparameters of control and, given this disclosure, the skilled artisanwill be able to determine suitable parameters to achieve desired valuesof x in the composition and desired phase or phases with desired degreesof crystallinity.

FIGS. 5A, 5B and 5C show additional molecular level views of compoundsof aluminum, boron and nitrogen in a continuous chemically bondednetwork having Al—N bonds and B—N bonds. In these examples, a substrate222 is silicon carbide that is covalently bonded to coating 224 a, 224 bor 224 c, respectively. In coating 224 a, the silicon atom of thesubstrate 222 is covalently bonded to two nitrogen atoms, which in turnare covalently bonded to a single boron atom. The boron atom is alsocovalently bonded to another nitrogen atom, which is also covalentlybonded to two aluminum atoms. Coating 224 b is similar, but the boronand aluminum atoms are transposed. In coating 224 c, the silicon atom ofthe substrate 222 is covalently bonded to two nitrogen atoms, which inturn are covalently bonded to a single boron atom. The boron atom isalso covalently bonded to another nitrogen atom, which is alsocovalently bonded to a single aluminum atom rather than two nitrogenatoms as in coating 224 a.

FIGS. 6A and 6B show additional molecular level views of compounds ofaluminum, boron and nitrogen in a continuous chemically bonded networkhaving Al—N bonds and B—N bonds. In these examples, a substrate layer322 is silicon carbide that is covalently bonded to coating 324 a and324 b, respectively. In these examples, the substrate layer is one layeramong a plurality of layers and is itself on a boron nitride layer 325.In coating 324 a, the silicon atom of the substrate layer 322 iscovalently bonded to two nitrogen atoms, which in turn are covalentlybonded to a single aluminum atom. The aluminum atom is also covalentlybonded to another nitrogen atom, which is also covalently bonded to aboron atom. The coating 324 b is similar but the boron and aluminumatoms are transposed.

Although a combination of features is shown in the illustrated examples,not all of them need to be combined to realize the benefits of variousembodiments of this disclosure. In other words, a system designedaccording to an embodiment of this disclosure will not necessarilyinclude all of the features shown in any one of the Figures or all ofthe portions schematically shown in the Figures. Moreover, selectedfeatures of one example embodiment may be combined with selectedfeatures of other example embodiments.

The preceding description is exemplary rather than limiting in nature.Variations and modifications to the disclosed examples may becomeapparent to those skilled in the art that do not necessarily depart fromthe essence of this disclosure. The scope of legal protection given tothis disclosure can only be determined by studying the following claims.

What is claimed is:
 1. An article comprising: a monolithic substrateselected from the group consisting of graphite, silicon carbide, siliconcarbide nitride, silicon nitride carbide, and silicon nitride; and acoating on the monolithic substrate, the coating having a free, exposedsurface and including a compound of aluminum (Al), boron (B) andnitrogen (N) in a continuous chemically bonded network having Al—N bondsand B—N bonds, wherein the compound includes an atom of nitrogencovalently bonded to an atom of boron and an atom of aluminum, and thecompound has a composition B_(x)Al_((1-x))N, where x is 0.001 to 0.999.2. The article as recited in claim 1, wherein the coating and themonolithic substrate are covalently bonded together.
 3. The article asrecited in claim 2, wherein the monolithic substrate is silicon carbide.4. The article as recited in claim 1, wherein the coating includes anamount of B—N, by weight, of no greater than 50%.
 5. The article asrecited in claim 1, wherein the coating includes an amount of B—N, byweight, of no greater than 10%.
 6. The article as recited in claim 1,wherein the Al—N and B—N are dispersed in the coating as of domains ofAl—N and B—N that have an average maximum domain size of one-hundrednanometers or less.
 7. The article as recited in claim 6, wherein theAl—N and B—N are in a ratio, by weight, of 90:10 to 50:50.
 8. Thearticle as recited in claim 7, wherein the ratio is from 75:25 to 50:50.9. The article as recited in claim 1, wherein the continuous chemicallybonded network has a homogenous distribution of the Al—N bonds and theB—N bonds.
 10. The article as recited in claim 1, wherein the Al—N bondsand the B—N bonds are molecularly distributed such that the continuouschemically bonded network has a nanodispersion of domains of the Al—Nbonds and the B—N bonds.
 11. The article as recited in claim 1, whereinthe coating has a uniform thickness and consists of the compound ofaluminum (Al), boron (B) and nitrogen (N).
 12. The article as recited inclaim 1, wherein, by weight percentage, the coating includes a greateramount of aluminum (Al) than boron (B).